Question

How do I determine whether a compound has dipole-dipole attractions, London Dispersion Forces, or Hydrogen Bonding when given the compound formula?

Answer 1

We first check polarity of bonds in molecule

A bond is polar if two atoms has high electronegative differnece , example Na-Cl bond is polar while C-H bond is non polar.

We then check overall polarity of molecule , symmetrical molecules even though it has polar bonds overall polarity will be zero , example CO2 is non polar while C-O bond is polar . SF6 is non polar.

If overall molecule is polar then it will have dipole-dipole as intermolecular forces

Hydrogen bonding is case happens when H is attached to high electro negative elements like F , Cl , O

Examples are molecules like NH3 , HF , H2O

Non polar molecules will have London dispersion forces as majorintermoecular forces

examples N2 , H2 , CH4 , alkanes ,